IEEE802.11 system is a system based on competition, and the adopted strategy of instant type response (“ACK”) is simple and effective. For example, ACK strategy is widely used in IEEE 802.11a/b/g, namely, ACK frame is sent back immediately when a station receives a unicast frame (such as DATA frame). The IEEE 802.11n systems have employed HT (High Throughput) Block ACK mechanism to acknowledge batches of data packets, which improves system efficiency. Especially, the block ACK strategy of HT immediate-type is a high-efficiency Block ACK mechanism among HT stations, namely, when a HT station have sent one batch of aggregate frames and its ACK policy position carried is set as normal ACK, by default the system adopts the immediate-type ACK policy. In addition, IEEE 802.11n also the defines delaying-type ACK strategy, if a system adopts the delaying-type ACK, the time delay of packet transmission can increase, which may be adverse to transmitting latency sensitive operations.
Among the existing communication systems based on centralized scheduling, such as, in IEEE 802.16 and long-term evolution (Long Term Evolution is called for short LTE) systems, all have employed the hybrid automatic repeat-request (HARQ-ACK) mechanism. HARQ mechanism acknowledges based on Physical Resource Block. Thus, timeliness and validity may be guaranteed. However, this unavoidably increases the complexity of implementation, and compared with other ACK mechanism of the MAC level of IEEE 802.11 systems, its reliability may also be greatly reduced.
Downlink HARQ mechanism of LTE system is briefly described as follows. The Downlink channel of the system comprises control signals, reference signals, and data signals. Wherein, Downlink data signals transmitted in Physical Downlink Shared Channel (PDSCH), and Packet Data Control Channel (PDCCH) transmits data transmission scheduling results. Uplink signal also comprises control signals and data signals. Physical Uplink Shared Channel (PUSCH) can be used for transmitting uplink control signals, including ACK/NACK, CQI indication signals etc. HARQ-ACK mechanism in LTE system acknowledges based on physical sub-frames, and the RLC layer of the LTE system needs comparatively complicated segmentation and recombination to adapt to Transmission Block (TB) of the physical layer.
In IEEE 802.16 systems also uses H-ARQ strategy. It is necessary to apply comparatively complicated segmentation method to form HARQ sub-packets. H-ARQ acknowledges based on HARQ sub-packets. In a word, HARQ causes the relatively low reliability of system and high implementation complexity, with increased effectiveness. The MAC layer of 802.16 systems have employed optional ARQ strategies, but owing to the need to dispatch ACK as an uplink data frame, the acknowledgement efficiency may be low with relatively long delays. Such systems, however, may be less complex to implement.
The ARQ function of the MAC layer of 802.16 systems is optional, and the scheduling of ACK is not instant, which causes long delays and complex implementations. Meanwhile, the ARQ requires acknowledgment of the ARQ-BLOCK, and ARQ-BLOCK sub-packet needs to be segmented, which may cause the efficiency of frame acknowledgment to be lower.